How to Send an Image from a Java Socket Client to a Server

The article builds on a previous example of bidirectional string communication using Java sockets and adds a concrete method for transferring binary image data.

Server side

A static method getImageFromClient() creates a ServerSocket listening on port 8088, accepts a client connection, and reads the incoming byte stream into a 2 KB buffer. The data is written to D:\badao.png until readLength equals -1, after which all streams and sockets are closed.

public static void getImageFromClient() throws IOException {
    byte[] byteArray = new byte[2048];
    ServerSocket serverSocket = new ServerSocket(8088);
    Socket socket = serverSocket.accept();
    InputStream inputStream = socket.getInputStream();
    int readLength = inputStream.read(byteArray);
    FileOutputStream imageOutputStream = new FileOutputStream(new File("D:\\badao.png"));
    while (readLength != -1) {
        imageOutputStream.write(byteArray, 0, readLength);
        readLength = inputStream.read(byteArray);
    }
    imageOutputStream.close();
    inputStream.close();
    socket.close();
    serverSocket.close();
}

Client side

The client defines sendImageToServer(), which opens the local image file C:\Users\admin6\Desktop\gzh.png via a FileInputStream, connects to the server at localhost:8088, and streams the file contents using the same 2 KB buffer. After the loop finishes, the output stream, file stream, and socket are closed.

public static void sendImageToServer() throws IOException {
    String imageFile = "C:\\Users\\admin6\\Desktop\\gzh.png";
    FileInputStream imageStream = new FileInputStream(new File(imageFile));
    byte[] byteArray = new byte[2048];
    System.out.println("socket begin =" + System.currentTimeMillis());
    Socket socket = new Socket("localhost", 8088);
    System.out.println("socket end =" + System.currentTimeMillis());
    OutputStream outputStream = socket.getOutputStream();
    int readLength = imageStream.read(byteArray);
    while (readLength != -1) {
        outputStream.write(byteArray, 0, readLength);
        readLength = imageStream.read(byteArray);
    }
    outputStream.close();
    imageStream.close();
    socket.close();
}

Execution order

First run the server’s main method to start listening, then run the client’s main method. After the transfer completes, the image appears at the specified server path (e.g., D:\badao.png), confirming successful binary transmission.

An illustrative GIF shows the process and the resulting file on the server.